| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a high-strength hot-rolled steel sheet having both strength and stretch flangeability; and to provide a method for producing the high-strength hot-rolled steel sheet. <P>SOLUTION: The high-strength hot-rolled steel sheet has a tensile strength of 780 MPa or more and excellent stretch flangeability. The high-strength hot-rolled steel sheet has a composition containing more than 0.035% but 0.055% or less of C, 0.2% or less of Si, 0.35% or less of Mn, 0.03% or less of P, 0.03% or less of S, 0.1% or less of Al, 0.01% or less of N, 0.08-0.25% (inclusive) of Ti, and 0.0005-0.0035% of B (inclusive) including 0.0005% or more of solid-solved B, with the balance made up of Fe and unavoidable impurities. The high-strength hot-rolled steel sheet has a matrix that contains a ferrite phase in an area ratio of more than 95% and a structure wherein Ti carbide particles having an average particle diameter of less than 10 nm are finely precipitated in the crystal grains of the ferrite phase with the volume ratio of the Ti carbide particles being 0.0015-0.007 (inclusive). <P>COPYRIGHT: (C)2012,JPO&INPIT |
